The present invention relates generally to a scroll-type machine and more specifically to a scroll-type machine specifically adapted for use in either cryogenic applications utilizing helium as the refrigerant or as an air compressor.
The use of helium as a refrigerant is common in very low temperature applications. However, the cyclic compression of helium presents very unique problems with respect to compressor design because of the high temperatures encountered during the compression process; typically more than twice the temperature rise encountered with the use of more conventional refrigerants. In order to prevent possible damage to the compressor from these high temperatures, it is necessary to provide increased cooling thereto such as by circulating large quantities of oil through the compressor.
Compression of air also results in substantial temperature increases and in addition thereto presents problems of contamination because the air compression system is an open system as opposed to the closed systems generally used in refrigeration applications. Because an air compressor is drawing its suction gas from the atmosphere, various particulate matter as well as potentially corrosive vapor and gaseous contaminants may be cycled through the compressor. Accordingly, in these types of compressors, it is also desirable to circulate substantial quantities of lubricant through the compressor as well.
The present invention comprises a scroll compressor, which is specifically adapted for use in the compression of both helium and air which in addition to the conventional low pressure oil sump, also includes a second high pressure oil sump in the discharge chamber. The oil from the low pressure oil sump is circulated to the bearings and other moving parts in a manner similar to that of conventional scroll compressors. However, oil from the high pressure oil sump is directed through an external heat exchanger for cooling and then injected into the compression pockets to aid in cooling of the compressor as well as to assist in sealing of the wraps and lubricating same. An oil separator is provided in the discharge chamber of the compressor to remove at least a portion of the injected oil from the compressed gas to thereby replenish the high pressure oil sump. A unique level control arrangement is also provided to prevent excess accumulation of oil in the high pressure oil sump. Relatively large volumes of oil must be circulated in this manner to prevent overheating of the compressor during operation as well as to aid in lubrication thereof. It should be noted that in such cryogenic applications it is exceedingly important that the refrigerant (i.e. helium) be virtually oil free and hence it is common for such systems to employ multiple external oil separators to ensure complete removal of the oil injected during the compression process. This is also true in many applications in which compressed air is utilized.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.